Network services, such as firewalls, server load balancing, etc., are value-added features that are commonly added to a computer network in the form of specialized appliances. These standalone appliances typically depend on the physical topology of the network and are not a fully integrated solution, have limited scalability, and add unnecessary complexity to network management. In addition, current network design is primarily ad-hoc, generally with no central control and management and no clear boundaries or admission control, often making it difficult to deploy new network services and security policies.